1. Field of the Invention
The present invention relates to a valve train for an internal combustion engine, and more particularly to a valve train for a multi-cylinder internal combustion engine including a plurality of cylinders in which valve operating characteristics of the respective cylinders are made different.
2. Description of the Related Art
There are proposed techniques for improving the fuel economy of a multi-cylinder engine including a plurality of cylinders by making valve operating characteristics of the respective cylinders different and stopping the actuation of inlet and exhaust valves of part of the cylinders, for example, when the engine is run at low speeds (refer to JP-A-2002-155712).
[Patent Literature No. 1]
JP-A-2002-155712
However, in the event that the constructions of the valve mechanisms provided for the plurality of cylinders are made different in order to make the operating characteristics of the valve mechanisms of the respective cylinders, it is considered that there is caused between the cylinders a difference in amount of lift of cams transmitted to valves which cams are formed on a common camshaft in such a manner as to correspond to the respective cylinders.
This is because when connection switching members are provided on rocker-arms provided between cams and valves of part of the cylinders so that the connection switching members are actuated in accordance with operating conditions of the engine to thereby enable a connection or disconnection between the cams and the valves, due to securing the smooth operation of the switching member for convenient, a locking error between the cams and valves has to be increased when compared with a case where there is provided no such switching member.
In addition, in a case where the rigidity of rocker-arms has to be made different for each cylinder for a convenient layout, because rocker-arms having a lower rigidity tend to deflect and deform largely, this can attribute to a possible cause for generating an error in locking conditions between the cams and the valves among the cylinders.
Namely, in the event that the construction or rigidity of the lift amount transmitting portions between the cams and the valves differs from cylinder to cylinder, there is caused a possibility that an actual valve lift amount differs from cylinder to cylinder. This can be a possible cause for generating a change in the revolution speed of the engine, in particular, when the engine is run at low rotational speeds.